The projection display device includes an optical unit that generates a video according to a video signal, and a projection lens for magnifying and projecting the video.
Recently, the projection display device further includes a lens shifting device that moves the projection lens in a predetermined direction intersecting an optical axis (hereinafter, referred to as video optical axis) where the projected video generated by the optical unit advances. Moving the projection lens enables movement of the projected video on a screen without moving the projection display device and reduction of formation of the projected video into a trapezoidal shape.
By keeping constant the angle between the video optical axis and the center axis of the projection lens during movement of the projection lens, the video is projected to the screen without any distortion. Thus, there has been offered a lens shifting device that smoothly moves the projection lens in astute where the angle between the video optical axis and the center axis of the projection lens is kept constant.
JP2007-33591A (hereinafter, referred to as Patent Literature 1) discloses a lens shifting device that includes a pair of guide shafts arranged on both sides of a projection lens and a plate including sliders corresponding to the guide shafts. The projection lens is fixed to the plate, and the plate moves along the guide shafts. By arranging the guide shafts on both sides of the projection lens with high positional accuracy in relation to the video optical axis, the positional accuracy between the center axis of the projection lens and the video optical axis is maintained, and the video can be projected to the screen without any distortion.
JP2003-315916A (hereinafter, referred to as Patent Literature 2) discloses a lens shifting device where the guide shafts of the lens shifting device disclosed in Patent Literature 1 are replaced with roller support mechanisms having rollers. Sliders are moved along the roller support mechanisms via the rollers, and accordingly sliding frictions between the sliders and the roller support mechanisms can be reduced.
JP2008-287292A (hereinafter, referred to as Patent Literature 3) discloses a lens shifting device that further includes a base brought into contact with the plate, and that presses the plate to the base by using the extension force of an elastic member such as a spring. The optical unit is fixed to the base. By pressing the base and the plate into contact with each other, the positional accuracy between the center axis of the projection lens and the video optical axis is kept, and the video can be projected to the screen without any distortion.
However, in the lens shifting device disclosed in Patent Literature 1 or Patent Literature 2, when the heavy projection lens is fixed to the plate, the guide shafts or the roller support mechanisms may be curved. As a result, the positional accuracy between the center axis of the projection lens and the video optical axis or the slidability of the sliders may deteriorate. To improve the rigidity of the guide shafts or the roller support mechanisms, the diameters of the guide shafts or the sizes of the roller support mechanisms must be increased. This creates a problem in which the size and weight of the lens shifting device increase.
A gap between the guide shaft or the roller support mechanism and the slider affects the positional accuracy between the center axis of the projection lens and the video optical axis and the sliding friction during movement of the plate. Processing accuracy is required for the guide shaft or the roller support mechanism, which increases costs.
Further, when a metal is used for the guide shaft in view of slidability and processing accuracy, due to heat generated by the use of the projection display device, thermal expansion or thermal contraction easily occurs in the guide shaft or the roller support mechanism. As a result, the gap between the guide shaft or the roller support mechanism and the slider changes, creating a problem in which there would be a reduction in positional accuracy or slidability.
In the lens shifting device disclosed in Patent Literature 3, by pressing the plate into contact with the base, the positional accuracy between the center axis of the projection lens and the video optical axis is kept. Thus, no improvement in accuracy is required for the gap between the guide shaft or the roller support mechanism and the slider. Further, since the plate is pressed to the base, there is no need to increase the rigidity of the guide shaft or the roller support mechanism. As a result, the lens shifting device can be constructed compact and lightweight.
However, in Patent Literature 3, the plate is pressed to the base by using the extension force of the elastic member. This generates sliding friction both between the plate and the base and between the plate and the elastic member, creating the possibility of a reduction in slidability. Slide contact members may be arranged both between the plate and the base and between the plate and the elastic member to achieve smooth sliding. However, this increases the number of components of the lens shifting device, consequently increasing the weight and the cost of the lens shifting device.
Further, the plate must be pressed from amide opposite the base by using the elastic member. Consequently, the structure may become complex.
Grease can be applied to the sliding portion to increase slidability. However, the grease may scatter with the temperature increase of the projection display device and may adhere to an optical component disposed in the projection display device. As a result, the quality of the projected video may be greatly reduced.